The proximal row of the wrist contains the scaphoid, the lunate, and the triquetrum. There is fourth bone called pisiform which is counted as bone in proximal row but is a sesamoid bone enclosed in the sheath of the flexor carpi ulnaris tendon and does not belong directly to the proximal carpal row.
The term ‘intercalated segment’ refers to it being the part in between the proximal segment of the wrist consisting of the radius and the ulna and the distal segment, represented by the distal carpal row and the metacarpals.
The three bones of the proximal carpal row form what is regarded by many authors as an intercalated segment between the radius and the distal row.
This intercalated segment is the the keystone in the coordination of motions of the wrist as well as in the control of forces that are transmitted from the hand to the forearm and vice versa.
The three proximal row bones namely scaphoid, lunate and triquetrum continuously need to adapt their position and orientation to guarantee the necessary joint congruency between the radius and distal row.
This further depends on geometry and the integrity of the ligaments that connect the three bones to each other and to the surrounding bones.